Soil-mixing or jet-grouting are ground improvement techniques used to increase the strength and reduce the permeability of soils in-situ. The desired compressive strength of this treated soil or soil-cement may be between 50 and 500 psi. In order to ensure that the desired consistency of the soil is obtained and to provide general quality control, the soil-cement is sampled, inspected and tested. Tests to determine the unconfined compressive strength and permeability are routinely performed and the quality of the mixing is determined by inspection of the recovered samples. Obtaining quality, continuous soil-cement samples is difficult, particularly when the soil-cement has relatively low strength, less than 150 psi.
Conventional methods of sampling soil cement include methods similar to core drilling used to recover samples of soft rocks. However, these methods can damage the sample and affect the integrity of the soil-cement sample obtained. Further, for low strength soil cements (e.g., less than 150 psi), or soil cements with gravel, it is difficult to obtain any representative samples by coring. For instance, low strength soil-cements are weak and are not strong enough to survive the coring process. The sample disintegrates inside the core barrel as the core bit tries to advance through the soil-cement. When gravel is present in the soil-cement it is significantly stronger than the soil-cement surrounding it and it requires considerable more effort to core the gravel than the soil-cement matrix. While trying to core through the gravel the weak soil-cement is eroded away from the gravel and soon loose pieces of gravel are rotating in the core barrel. These loose pieces of gravel completely destroy the soil-cement core.
Another method of obtaining a soil-cement sample involves wet grab sampling of the recently mixed soil-cement at depth. While still fluid, a volume of the soil-cement is recovered and placed into molds for curing and later testing. However, the curing of the soil-cement does not take place in the ground (i.e., the actual conditions of the soil-cement in use) and thus could affect results. Further, wet grab samples do not provide a continuous treated soil-cement sample for an entire depth of the soil improvement. Accordingly, it can not be relied on to evaluate the quality of the mixing.
Accordingly, a device and method of obtaining a continuous soil-cement sample over the depth of the improved soil would be advantageous.